Lecture Notes Flashcards

Somatosensation and Special Senses

• Somatosensation includes touch, proprioception, and pain.
• Special senses include vision and taste.
• Each special sense has a similar basic layout and key components.

Key Components of Special Senses

• Specialized Receptor Cell:
  • Each special sense has a specialized receptor cell.
  • These cells have receptors embedded in their membrane.
  • Receptors are activated by specific stimuli (e.g., photons of light, chemicals).
• Sensory Neuron:
  • Carries information to the brain.
• Pathway to Cortex:
  • Information is relayed to the central nervous system and then to the cortex.

Taste (Gustation)

Anatomy of the Tongue

• The tongue is covered in bumps called papillae.
• Four types of papillae:
  • Valate (Circumvalate):
    • Large, dome-shaped.
    • Have many taste buds.
  • Fungiform:
    • Mushroom-shaped.
    • Have taste buds but fewer than valate papillae.
  • Foliate:
    • Have taste buds.
  • Filiform:
    • Do not have taste buds.
    • Contribute to texture and temperature sensations.
    • Important for the flavor of food.

Taste Buds and Gustatory Cells

• Taste buds are located on the sides of papillae (except filiform).
• Taste buds contain multiple gustatory cells.
• Gustatory cells are specialized receptor cells for taste.
• They have chemoreceptors in their membranes.
• Chemoreceptors are activated by chemicals in food, leading to taste sensations.

Five Basic Taste Sensations

• Sweet:
  • Activated by simple sugars like glucose and fructose.
  • Sugars bind to sweet chemoreceptors.
• Sour:
  • Activated by hydrogen ions (H+).
  • High hydrogen ion concentration indicates acidity.
  • H^+ ions bind to and activate sour chemoreceptors.
• Salty:
  • Activated by sodium ions (Na+).
  • Na^+ ions bind to and activate salty chemoreceptors.
• Bitter:
  • Activated by various nitrogen-containing compounds, which are often found in poisonous substances.
• Umami:
  • Savory, meaty flavor.
  • Caused by amino acids like glutamate.
  • Amino acids bind to umami chemoreceptors.

Steps of Transduction

• Chemical Stimuli:
  • Chemicals (e.g., sodium ions, amino acids) bind to chemoreceptors on gustatory cells.
• Ion Flux and Depolarization:
  • Binding of chemicals causes a change in ion flux (e.g., opening of sodium channels).
  • Influx of ions leads to local depolarization.
• Voltage-Gated Calcium Channels:
  • Depolarization activates voltage-gated calcium channels.
  • Ca^{2+} influx of calcium ions triggers neurotransmitter release.
• Neurotransmitter Release:
  • Gustatory cells release neurotransmitters to sensory neurons.
• Action Potential in Sensory Neuron:
  • Neurotransmitter binding causes depolarization and action potential in the sensory neuron.
• Nerve Transmission:

AXONS
* Axons of sensory neurons form nerves.

CRANIAL NERVES
* Taste information is carried to the brain by cranial nerves:
* Facial nerve (VII): Anterior two-thirds of the tongue.
* Glossopharyngeal nerve (IX): Posterior one-third of the tongue.
* Vagus nerve (X): Taste buds in the oral cavity.

Pathway to the Brain

• Cranial Nerves:
  • VII (Facial), IX (Glossopharyngeal), or X (Vagus) carry sensory information.
• Brain Stem:
  • First stop: Solitary nucleus in the medulla. The medulla is part of the brainstem which includes the midbrain, the pons and the medulla.
• Thalamus:
  • Relay station for sensory information.
• Cortex:
  • Primary gustatory cortex in the parietal lobe.

Auditory System

Structure of the Ear

• External Ear (Outer Ear):
  • Structures before the eardrum.
• Middle Ear:
  • From eardrum to the cochlea.
• Inner Ear:
  • Cochlea.

Key Structures

• Tympanic Membrane (Eardrum):
  • Boundary between outer and middle ear.
  • Vibrates with air pressure (sound waves).
• Ossicles:
  • Three small bones in the middle ear: Malleus, Incus, Stapes.
  • Malleus (hammer) is connected to the tympanic membrane.
  • Incus.
  • Stapes is connected to the oval window of the cochlea.
  • Amplify and convert sound waves from air waves to fluid waves.
• Cochlea:
  • Spiral-shaped structure filled with fluid.
  • Contains three chambers; the middle one is the cochlear duct.
  • H_20
  • Cochlear Duct:
    • Middle chamber of the cochlea.
    • Floor is called the basilar membrane.
    • Contains the organ of Corti.
  • Organ of Corti:
    • Located on the basilar membrane. Specialized receptor cells are found inside the organ of Corti.
    • Converts energy from waves to electrical impulses.

Organ of Corti

• Hair Cells:
  • Specialized receptor cells for the auditory system.
  • Have mechanoreceptors that are physically opened by pressure.
• Tectorial Membrane:
  • Stiff structure that acts as a roof above the hair cells.

Steps of Transduction

• Sound Waves:
  • Waves in the air travel through the ear and cause vibrations.
• Basilar Membrane Movement:
  • Waves cause the basilar membrane (the floor) to move.
• Hair Cell Bending:
  • As the basilar membrane moves, hair cells bump into the tectorial membrane (the roof), causing them to bend.
  • The hairs on the cells(stereocilia) bend due to these movements.
• Mechanoreceptor Activation:
  • Mechanical bending activates mechanoreceptors on hair cells.
  • Mechanically opens ion channels.
• Neurotransmitter Release:
  • Leads to neurotransmitter release.
  • Depolarization leads to neurotransmitter release.
  • Neurotransmitter activates a sensory neuron whose axons travel in a bundle to the brain.
• Nerve Transmission
  • Sensory neuron axons form cranial nerves.
  • Vestibulocochlear nerve (VIII) carries auditory information. Cranial nerve 8 or vestibulocochlear nerve is responsible for sending auditory signals.

Pathway to the Brain

• Cranial Nerve:
  • Vestibulocochlear nerve (VIII).
• Brain Stem:
  • Multiple stops:
    • Cochlear nuclei (medulla)
    • Superior olivary nucleus (pons) - for sound localization
  • Sound information travels gradually up the brainstem.
• Thalamus:
  • Relay station.
• Cortex:
  • Primary auditory cortex in the superior temporal lobe of the temporal lobe.